1. Problem

For a given number n for example (1234), write a Java program to reverse the number (4321 in this case).

2. Steps reverse a number

Here are the steps to reverse a number:

• Initialize a variable to store the reversed number:
  • Start with reversedNumber = 0.

int reversedNumber = 0;

• Extract digits from the original number:
  • Use the modulo operator (%) to get the last digit of the number.
  • Add this digit to the reversed number after multiplying the reversed number by 10 (to shift the digits to the left).
  • Remove the last digit from the original number by dividing it by 10 (using integer division).

while (number != 0) {
    int digit = number % 10;                        // Get the last digit
    reversedNumber = reversedNumber * 10 + digit;   // Add the digit to reversedNumber
    number = number / 10;                           // Remove the last digit
}

• Return the reversed number:
  • Once the original number becomes 0, the reversed number is ready.

return reversedNumber;

3. Program

public class ReverseNumber {

    public static int reverse(int number) {
        int reversedNumber = 0;

        while (number != 0) {
            int remainder = number % 10;            // Get the last digit
            reversedNumber = reversedNumber * 10 + remainder;   // Add the digit to reversedNumber
            number /= 10;                       // Remove the last digit
        }

        return reversedNumber;
    }

    public static void main(String[] args) {
        int number = 1234;  // Example number to reverse
        int result = reverse(number);
        System.out.println("Reversed Number: " + result);  // Output: Reversed Number: 4321
    }
}